This invention relates to an electronic typewriter.
In a conventional electronic typewriter as shown in FIG. 1, a keyboard 4 on which an array of keys for generating key signals for specifying characters and various required functions is arranged on the front of a housing 2. If a key on the keyboard 4 is operated, a key signal is generated and the printing operation is effected in accordance with the key signal.
FIG. 2 illustrates the details of the keyboard 4, which contains various character keys 6 and various function keys 8. However, the key characters, key functions and key locations of an electronic typewriter differ depending on the country where it is used; therefore, it is necessary to make the keyboard in compliance with the specifications of that country. Such a problem as differences in key characters, key functions and key locations can be eliminated by changing the printing characters of a print wheel (not shown) and the arrangement of the key tops. However, it is necessary to discriminate a specific function which is provided by a certain character key from ordinary inherent functions of the character keys. Such a specific function includes for example: the function by which, when a particular character key is operated, a carriage (not shown) is held at the present location after the corresponding character has been printed; or the function by which, when a certain character key is kept pressed for more than a predetermined time period, the corresponding character is repeatedly printed, or the like. To provide such a difference between these functions, the following methods have been considered. For example, (1) changing the internal connections between the keyboard 4 and an associated control unit (not shown); (2) changing the content of a read only memory (ROM) in the control unit; or (3) coupling a switching circuit (not shown) for selection of the specifications to the control unit, or the like. However, according to the methods (1) and (2), it is required that the wiring of the keyboard 4 be changed in compliance with the specifications of the keyboard 4 and that ROMs with different contents be used. The method (3) has an advantage over methods (1) and (2) since all of the contents corresponding to the various specifications are stored in a single ROM and the content of the ROM is selected in compliance with desired specifications using a switching circuit for the selection of the specifications.
As is schematically shown in FIG. 3, for example, this method (3) is obtained by coupling a switching circuit 10 for selection of the specifications to an additional input port of a control unit 12 whose input and output ports are connected to return lines RL and scan lines SL of a keyboard matrix circuit 14, respectively. However, to execute this method (3), it is necessary to couple the switching circuit 10 for selection of the specifications to the control unit 12. Hence, for example, in the case where the keyboard matrix circuit 14 and a control section including the control unit 12 and the switching circuit 10 are formed individually on separate printed circuit boards, it is impossible to use the keyboard matrix circuit 14 which is so constituted as to have a different specification from the specification selected by the switching circuit 10. In other words, it is impossible to commonly utilize the control unit 12 for the keyboard matrix circuits constituted to have different specifications. Thus, attention must be paid to the assembling process so that the control unit 12 is suitably combined with the keyboard matrix circuit having the same specification as the control unit 12.
Moreover, in the case where the operational section of the switching circuit 10 is disposed on the keyboard 4, particular countermeasures must be taken to deal with the increase in the number of connectors and the electric noise. Also, an additional input port must be provided for the control unit 12 to employ this switching circuit 10.